anatomy of spinal cord...continuous above with the medulla oblongata. the tapered inferior end forms...
TRANSCRIPT
ANATOMY OF SPINAL CORD
By Khaleel Alyahya, PhD, MEdw w w . k h a l e e l a l y a h y a . n e t | @ k h a l e e l y a
D e p a r t m e n t o f A n a t o m y
C o l l e g e o f M e d i c i n e
K i n g S a u d U n i v e r s i t y
RESOURCES
Human Brain
By John Nolte
Essential of Human
Anatomy & Physiology
By Elaine Marieb and
Suzanne Keller
Gray’s Anatomy
By Richard Drake, Wayne
Vogl & Adam Mitchell
KENHUB
www.kenhub.com
Atlas of Human
Anatomy
By Frank Netter
Objectives
▪ Describe the external anatomy of the spinal cord.
▪ Describe the internal anatomy of the spinal cord.
▪ Describe the spinal nerves: formation, branches and distribution via plexuses.
▪ Define Dermatome and describe its significance.
▪ Describe the meninges of the spinal cord.
▪ Define a reflex and reflex arc and describe the components of the reflex arc.
By Khaleel Alyahya, PhD, MEd
Review
By Khaleel Alyahya, PhD, MEd
Functions
❑ COLLECTION OF SENSORY INPUT
▪ Identifies changes occurring inside and outside the body by using sensory receptors.
▪ These changes are called stimuli.
❑ INTEGRATION
▪ Processes, analyses & interprets these changes and makes decisions.
❑ MOTOR OUTPUT
▪ It then effects a response by activating muscles or glands (effectors) via motor output.
By Khaleel Alyahya, PhD, MEd
Organization
Structural
❑ Central Nervous System (CNS)
▪ Brain & Spinal Cord
❑ Peripheral Nervous System (PNS)
▪ Nerves & Ganglia
• Cranial nerves
• Spinal nerves
Functional
❑ Sensory Division (Afferent)
❑ Motor Division (Efferent)
▪ Autonomic
▪ Somatic
By Khaleel Alyahya, PhD, MEd
Terms
By Khaleel Alyahya, PhD, MEd
GANGLION A GROUP OF NEURONS
OUTSIDE THE CNS
NUCLEUSA GROUP OF NEURONS
WITHIN THE CNS
NERVEA GROUP OF NERVE FIBERS (AXONS) OUTSIDE THE CNS
TRACT A GROUP OF NERVE FIBERS (AXONS) WITHIN THE CNS
Spinal Cord
By Khaleel Alyahya, PhD, MEd
Introduction
▪ The main pathway for information connecting the brain and peripheral nervous system.
▪ It is elongated, cylindrical, suspended in the vertebral canal and protected by vertebrae
▪ Surrounded by the meninges and cerebrospinal fluid (CSF).
▪ The primary function of spinal cord is a transmission of neural signals between
the brain and the rest of the body.
• Sensory
• Motor
• Local reflexes
By Khaleel Alyahya, PhD, MEd
Structures
▪ Extends from foramen magnum to 2nd lumbar vertebra.
▪ Continuous above with the medulla oblongata.
▪ The tapered inferior end forms conus medullaris.
▪ It is connected to the coccyx by a non-neuronal cord called Filum Terminale.
▪ Gives rise to 31 pairs of spinal nerves
▪ The bundle of spinal nerves extending inferiorly from lumbosacral enlargement and
conus medullaris surround the filum terminale and form cauda equina
▪ Segmented
• 8 Cervical
• 12 Thoracic
• 5 Lumbar
• 5 Sacral
• 1 Coccygeal
▪ Two enlargements:
• Cervical Enlargement: supplies upper limbs.
• Lumbosacral Enlargement: supplies lower limbs.
By Khaleel Alyahya, PhD, MEd
Cross Section
▪ The spinal cord is incompletely divided into two equal parts, anteriorly by a short,
shallow median fissure and posteriorly by a deep narrow septum, the posterior
median sulcus.
▪ Composed of grey matter in the center surrounded by white matter supported by
neuroglia.
▪ Commissures: connections between left and right halves
• Gray with central canal in the center
• White
▪ Roots: spinal nerves arise as rootlets then combine to form roots
• Dorsal (posterior) root has a ganglion
• Ventral (anterior)
• Two roots merge latera
By Khaleel Alyahya, PhD, MEd
Grey Matter
▪ The arrangement of grey matter in the spinal cord resembles the shape of the letter H.
▪ Having:
• two posterior horns
• two anterior horns
• two lateral horns/columns.
▪ Consists of:
• nerve cell bodies and their processes
• neuroglia
• blood vessels
By Khaleel Alyahya, PhD, MEd
Grey Matter
▪ The nerve cells are multipolar, and are of THREE main categories:
Sensory neurons (Tract cells)
• receive impulses from the periphery of the body and whose axons constitute the ascending
fasciculi of the white matter.
• located in the dorsal horns.
Lower motor neurons
• transmit impulses to the skeletal muscles.
• located in the ventral hornso similar neurons in the lateral horn are the preganglionic neurons of the autonomic system.
Interneurons (connector neurons)
• linking sensory and motor neurons, at the same or different levels, which form spinal reflex
arcs.
By Khaleel Alyahya, PhD, MEd
Spinal Cord Nuclei
The prominent nuclei (groups of neuron cell bodies) in the spinal cord are:
▪ Marginal zone: located at the tip of the dorsal horn and is important for relaying pain and temperaturesensation to the brain. (Laminae I)
▪ Substantia gelatinosa: located at the top of the dorsal horn, It is important for relaying pain, temperatureand light touch sensation to the brain. It is composed of large neurons and found throughout the length ofspinal cord. (Laminae II)
▪ Nucleus proprius: located in the neck of the dorsal horn anterior to substantia gelatinosa, and it isconcerned with senses of position & movement. Also composed of large neurons and found throughout thelength of spinal cord. (Laminae IV)
▪ Dorsal nucleus of Clarke: the most dorso-medial nuclei, and it relays unconscious proprioceptiveinformation to the brain. Only found in spinal segments C8 to L3. (Laminae VII)
▪ Interomediolateral nucleus: located in the intermediate column and lateral horn, and it relays sensoryinformation from viscera to the brain, and autonomic signals from the brain to the visceral organs. (LaminaeVII)
▪ Lateral motor neurons and medial motor neurons: located in the ventral horn. Composed ofmotor neurons that innervate visceral and skeletal muscles. (Laminae VIII & IX)
By Khaleel Alyahya, PhD, MEd
Rexed Laminae
▪ It is an alternative to spinal cord nuclei where cells were grouped according to
their structure and function, rather than solely on location.
▪ Identified in the early 1950s by Swedish neuroscientist.
▪ Cells of the same type are clustered into groups, which occur in long columns
▪ In transverse section, these columns appear as layers, especially within the dorsal
horn
▪ These layers are called the laminae of Rexed that are numbered by Roman
numerals, starting from the tip of the dorsal horn and moving ventrally into the
ventral horn.
By Khaleel Alyahya, PhD, MEd
Motor Neurons in Ventral Horn
Large multipolar cells
▪ whose axons pass out in the ventral roots of spinal nerves as alpha efferent which
innervate extrafusal muscle fibers of skeletal muscles.
Small multipolar cells
▪ whose axons pass out in the ventral roots of spinal nerves as gamma efferent
which innervate intrafusal muscle fibers of neuromuscular spindles
By Khaleel Alyahya, PhD, MEd
White Matter
▪ Consists of mixture of nerve fibers, neuroglia and blood vessels.
▪ White color is due to high proportion of myelinated nerve fibers
▪ The white matter of the spinal cord is arranged in columns/funiculi; anterior,
posterior and lateral.
▪ The nerve fibers are arranged as bundles, running vertically through the cord.
▪ A group of nerve fibers (axons) that share a common origin, termination and
function form a tract or fasciculus
▪ These tracts are formed by sensory nerve fibers ascending to the brain, motor
nerve fibers descending from the brain and fibers of connector neurons.
▪ Tracts are often named according to their points of origin and destination, e.g.
spinothalamic, corticospinal.
By Khaleel Alyahya, PhD, MEd
White Matter
By Khaleel Alyahya, PhD, MEd
Commissures
Grey Commissure
▪ Transverse bridge of grey matter connecting the anterior and posterior gray horns
on each side
▪ It is pierced by the central canal that divides it into anterior and posterior parts
White Commissure
▪ Lies ventral to the gray commissure
▪ Mainly contains decussating nerve fibers
By Khaleel Alyahya, PhD, MEd
Central Canal
▪ The cerebrospinal-filled space that runs longitudinally through the entire length of
the spinal cord.
▪ Lined by ependyma (ciliated columnar epithelium)
▪ Continuous with the ventricular system of the brain
▪ Superiorly opens into the 4th ventricle
▪ Inferiorly in the conus medullaris, it expands into the fusiform terminal ventricle
and terminates below at the root of filum terminale
By Khaleel Alyahya, PhD, MEd
Regional Differences
▪ Although the general pattern of gray matter is the same throughout spinal cord,
regional differences are apparent in transverse sections
▪ The amount of white matter increases in a caudal-to-cranial direction because
fibers are added to ascending tracts and fibers leave descending tracts
▪ The gray matter is in increased volume in cervical & lumbosacral enlargements
for innervation of upper & lower limbs
▪ The lateral horn is characteristics of thoracic and upper lumbar segments
By Khaleel Alyahya, PhD, MEd
Cervical
Thoracic
Lumbar
Sacral
Spinal Nerves
▪ Thirty-one pairs of spinal nerves
▪ First pair exit vertebral column between skull and atlas, last four pairs exit via the
sacral foramina and others exit through intervertebral foramina
▪ Eight pair cervical, twelve pair thoracic, five pair lumbar, five pair sacral, one pair
coccygeal
▪ Each spinal nerve arises as rootlets which then combine to form dorsal (posterior)
& ventral (anterior) roots.
▪ Two roots merge laterally and form the spinal nerve.
▪ Dorsal (posterior) root has a ganglion (dorsal root/sensory ganglion) that contains
the cell bodies of the sensory neurons
▪ Each spinal nerve then divides into a smaller dorsal and a larger ventral ramus
By Khaleel Alyahya, PhD, MEd
Branches of Spinal Nerves
▪ Dorsal Ramus: innervate deep muscles of the trunk responsible for movements of
the vertebral column and skin near the midline of the back.
▪ Ventral Ramus: what they innervate depends upon which part of the spinal cord is
considered.
• Thoracic region: form intercostal nerves that innervate the intercostal muscles and the skinover the thorax
• Remaining spinal nerve ventral rami (roots of the plexus): form five plexuses (interminglingof nerves).
o Ventral rami of C1-C4 = cervical plexus
o Ventral rami of C5-T1 = brachial plexus
o Ventral rami of L1-L5 = lumbar plexus
o Ventral rami of L4-S4 = sacral plexus
o Ventral rami of S4 & S5 = coccygeal plexus
▪ Communicating Rami: communicate with sympathetic chain of ganglia.
By Khaleel Alyahya, PhD, MEd
Dermatomes
▪ Dermatome is a segment of skin supplied by one spinal nerve.
▪ Each of these spinal nerves relay sensation from a particular region of skin to the
brain.
▪ The nerves from the upper cervical spine supply the skin of the neck.
▪ C5 to T1 nerves supply the arms.
▪ T2 to L2 nerves supply the chest and abdomen.
▪ L3 to S1 nerves supply the skin of the legs.
▪ S1-C1 nerves go to the groin.
▪ Testing of dermatomes is part of the neurological examination looking for sensation
changes within a specific dermatome that may help in determining the pathological
disc level.
By Khaleel Alyahya, PhD, MEd
Spinal Meninges
▪ Connective tissue membranes surrounding spinal cord and brain
• Dura mater: continuous with epineurium of the spinal nerves
• Arachnoid mater: thin and wispy
• Pia mater: bound tightly to surface of brain and spinal cord.
o Forms the filum terminale, which anchors spinal cord to coccyx and the denticulate ligaments thatattach the spinal cord to the dura mater
▪ Spaces
• Epidural: Contains blood vessels, connective tissue and fat.
• Subdural: Contains serous fluid
• Subarachnoid: Contains CSF and blood vessels within web-like strands of arachnoid
tissue
By Khaleel Alyahya, PhD, MEd
Reflex & Reflex Arc
▪ A reflex is a rapid, involuntary, stereotyped pattern of response brought by
a sensory stimulus.
▪ A neural pathway mediating the reflex actions is called reflex arc.
By Khaleel Alyahya, PhD, MEd
Spinal Nerve Injury
▪ The spinal cord injury is the damage to the spinal cord that causes
temporary or permanent changes in the functions.
▪ Symptoms may include loss of muscle function, sensation,
or autonomic function.
▪ Injury can occur at any level of the spinal cord and can be complete injury
with a total loss of sensation and muscle function, or it can be incomplete
injury.
▪ Depending on the location and the severity of damage, the symptoms
could include numbness, paralysis or incontinence.
▪ Long term outcomes ranges widely from full recovery to
permanent quadriplegia or paraplegia.
▪ Complications can include muscle atrophy, pressure sores, infections,
and breathing problems.
By Khaleel Alyahya, PhD, MEd